The present invention relates generally to a control system for an internal combustion of an automotive vehicle, and more particularly, to a method and apparatus for predicting the exhaust gas temperature at a predetermined location of the exhaust system.
Minimizing tailpipe emission is an objective of closed loop fuel systems. Closed loop fuel systems include a catalytic converter that is used to treat the exhaust gas of an engine. Such converters operate to chemically alter the gas composition produced by the engine to help meet various environmental regulations governing tailpipe emissions. Determining the temperature of the catalytic converter is one feedback used in the control thereof.
The engine has an exhaust manifold that receives exhaust gases from the engine cylinders. The exhaust manifold routes the flow of exhaust gases into the exhaust system that includes the catalytic converter. The exhaust flange is the location where the exhaust manifold and exhaust system are joined. As is described in U.S. Pat. No. 5,956,941, which is incorporated by reference herein, the instantaneous temperature of the catalytic converter may be determined from the instantaneous temperature of the exhaust gas at the exhaust flange. The temperature of the catalyst is then provided to the engine controller to control the various engine operating parameters. It should also be noted that the flange temperature is also used to predict various other downstream predictions such as the front heated exhaust gas oxygen temperature, the catalyst inlet temperature, the catalyst midbed temperature, and the downstream heated exhaust gas oxygen sensor temperature.
It has been found that the exhaust flange temperature response exhibits second order behavior. That is, initially the measured temperature reacts at a fast rate with a zero to 20 second time constant and after that time, the rate slows considerably to a 50 to 250 second time constant. Known methods for determining the exhaust flange temperature do not take this into account and therefore may not be accurate at least over a portion of the temperature range.
Current catalyst temperature prediction algorithms are performed on an engine dynamometer with recalibration after the engine is placed into a vehicle during on road testing. Because the temperature determination may not be accurate as mentioned above, it has been found that about twenty percent of the dynamometer calibrations must be revised in on-road testing. This recalibration increases the cost and time of development.
It would therefore be desirable to provide a method and apparatus for more accurately determining the exhaust flange temperature.
The present invention provides a more accurate method and apparatus for determining the exhaust flange temperature over the operating range of the automotive vehicle.
In one aspect of the invention, a system for predicting the temperature of a catalyst including a control system and method for controlling an engine of an automotive vehicle having a catalyst and controller is set forth herein. The controller is configured to determine a first exhaust flow rate and a second exhaust flow rate based on a flow rate of the exhaust gases. The controller is further configured to determine a first temperature of exhaust gases associated with the first exhaust flow rate based on a steady state temperature and an amount of heat transferred from the exhaust gases associated with the first exhaust flow rate to an exhaust system. The controller is further configured to determine a second temperature of exhaust gases associated with the second exhaust flow rate based on the steady state temperature. The controller is further configured to determine the catalytic converter temperature based on the first temperature and the second temperature.
In a further aspect of the invention, a method for determining a temperature of an emission catalyst communicating with exhaust gases from an engine includes determining a first exhaust flow rate and a second exhaust flow rate based on a total flow of the exhaust gases, determining a first temperature of exhaust gases associated with the first exhaust flow rate based on a steady state temperature and an amount of heat transferred from the exhaust gases associated with the first exhaust flow rate to an exhaust system, determining a second temperature of exhaust gases associated with the second exhaust flow rate based on the steady state temperature, and determining the catalyst temperature based on the first temperature and the second temperature.
One advantage of the invention is that development time and cost of the engine is reduced because post-dynamometer calibration of the flange temperature may be significantly reduced or eliminated.
Other advantages and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.